Add ignore read on reservedIpRange field Filestore Instance

[modular-magician]

When using connectMode=PRIVATE_SERVICE_ACCESS, the returned value won't match the sent value as the returned value is an IP range from the provided named range.

It should be safe to ignore read on this field as it is immutable after instance creation.

Fixes #12877
b/257089398

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Release Note Template for Downstream PRs (will be copied)

filestore: fixed a bug causing premadiff on `reserved_ip_range` field in `google_filestore_instance`

Derived from GoogleCloudPlatform/magic-modules#8520

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